It might not be the way you undertand it, but it is how it works physically. It's all relative. Most people don't understand much of what Einstein did. Is either photon actually moving faster than light? No.

Boba, here's a straight answer to the scenario you've described:

https://www.physicscentral.com/experiment/askaphysicist/physics-answer.cfm?uid=20130130105151

And btw, having the photons moving toward, or away from each other, poses the exact same problem

Let's apply this formula to the case in your question, when v itself is equal to the speed of light c. In that case,

vrelative =2c/[1 + 1] = 2c/2 = c.

So the photons are not moving away from each other at twice the speed of light. Instead, their relative velocity is still just c.

 

Actually the special theory of relativity isn't about the actual speed of light.

Special relativity is fundamentally about the speed of light. Special relativity was introduced in a paper called "On the electrodynamics of moving bodies" in which Einstein makes two postulates: 1) the invariance of physical laws with respect to reference frame, and 2) the invariance of the vacuum speed of light. Given these two postulates and following the logical consequences, all of special relativity -- including the Lorentz transformations -- falls out. The speed of light is essential to relativity.

In fact, E = mc^2 isn't correct. It's a reduced formula from a larger original formula that accounts for the specifics of light itself, which e=mc^2 does not. Those parts of the equation simply cancel out when referring to mass, not light.

There are as many mass-energy equivalence equations as there are ways of defining energy and mass. Which equation is "correct" depends on the context, but there is nothing incorrect about E = mc^2, just as there's nothing incorrect about E = sqrt( (mc^2)^2 + (pc)^2), where p is momentum. It's just easier to remember E = mc^2 as the canonical mass-energy equivalence relation.

E does not in fact = mc^2. Because Mass is not a property of energy,. Energy can exist without mass (and does). Energy is a property of mass. Mass cannot exist without energy. This is probably the most fundamental concept anyone in physics should ever grasp.

Mass is not a property of energy, nor is energy a property of mass. They are equivalent (modulo scale factor) ways of characterizing a single physical property. Forget the idea that energy cannot exist without mass, as that would imply that "pure" energy is unaffected by gravity fields, which is clearly not the case. While it's true that light has no rest mass, it's only true by definition: rest mass is the energy that would be measured in the object's rest frame, but light has no rest frame. Wondering about the rest mass of of a photon is like wondering about the color of the invisible man.

Having said that, it is true that the speed of light can be exceeded- shine two flashlights at each other (as you were mentioning), and voila, one of the photos as related to another photon headed in the opposite way is indeed moving twice as fast, if the other photon is motionless. A realworld example this is the blue-shift in certain nuclear reactors.

No, no, no. Google the two flashlights example and you'll find a million references showing why this is wrong.

 

Special relativity is fundamentally about the speed of light. Special relativity was introduced in a paper called "On the electrodynamics of moving bodies" in which Einstein makes two postulates: 1) the invariance of physical laws with respect to reference frame, and 2) the invariance of the vacuum speed of light. Given these two postulates and following the logical consequences, all of special relativity -- including the Lorentz transformations -- falls out. The speed of light is essential to relativity.


There are as many mass-energy equivalence equations as there are ways of defining energy and mass. Which equation is "correct" depends on the context, but there is nothing incorrect about E = mc^2, just as there's nothing incorrect about E = sqrt( (mc^2)^2 + (pc)^2), where p is momentum. It's just easier to remember E = mc^2 as the canonical mass-energy equivalence relation.


Mass is not a property of energy, nor is energy a property of mass. They are equivalent (modulo scale factor) ways of characterizing a single physical property. Forget the idea that energy cannot exist without mass, as that would imply that "pure" energy is unaffected by gravity fields, which is clearly not the case. While it's true that light has no rest mass, it's only true by definition: rest mass is the energy that would be measured in the object's rest frame, but light has no rest frame. Wondering about the rest mass of of a photon is like wondering about the color of the invisible man.


No, no, no. Google the two flashlights example and you'll find a million references showing why this is wrong.

I drew up a really good graphic illustrating how two people moving at different speeds would measure the speed of light to be the same in both cases. Not sure if i can find it but i'll look. It's a graphic of a moving bus with a light beam shining in the front window and traveling through the bus. The guy on the ground sees the same light speed as the guy in the bus even though the bus is moving.

 

I drew up a really good graphic illustrating how two people moving at different speeds would measure the speed of light to be the same in both cases. Not sure if i can find it but i'll look. It's a graphic of a moving bus with a light beam shining in the front window and traveling through the bus. The guy on the ground sees the same light speed as the guy in the bus even though the bus is moving.

Cool.

One of the standards ways to show this is with Minkowski diagrams

https://owlcation.com/stem/Minkowski-Diagram

 

Cool.

One of the standards ways to show this is with Minkowski diagrams

https://owlcation.com/stem/Minkowski-Diagram

Click the thumbnail above to see the illustration.
Note how the two photons appear at the same place on both rulers according to their respective scales. For example, when the top photon is at position 3 on the stationary ruler the bottom photon is also at position 3 but on the moving ruler.

I found my article from How Stuff Works, amazingly i drew the diagram exactly 18 years ago to the day, 08/07/2001 !
Anyway, this is interesting as it is a direct illustration without any angles and so forth.
I remembered wrong though, it's two flashlights being turned on at the same time at the back of two different buses, one parked and the other traveling at 0.87 times the speed of light. They both have the same rulers inside too but see what takes place in the drawing.
The text reads as follows here...I call this the "Synchronicity of Light and Objects".

There have been quite a few questions with regard to riding on a
fast moving vehicle and shining a flashlight directed forward.
The questions always involve trying to understand why the light
doesnt travel at the speed of light PLUS the speed of the vehicle
(the sum of the two speeds). I'm convinced that a good way
to explain this phenomenon is with a series of slides showing
graphically what really happens. Sometimes words just arent enough.
Here is a graphical illustration of light traveling from a source
at rest as compared to light traveling from a source in motion.

In a nutshell, once a photon is created it travels at the speed of
light and exists in a world all its own, traveling as if it knows
nothing of any other moving objects, unless of course it hits one.
Since we arent immediately concerned with photons striking objects,
we wont discuss that aspect of photon travel.

In this experiment, we analyze two separate photons that are released
from two special flashlights that emit exactly one photon each when
told to do so, and we tell them to do so at the same point in space.

We use two imaginary buses in which the flashlights are mounted.
One bus will be still and the other bus will be traveling
at 0.87 times the speed of light. We mount the flashlights at the
very back of each bus, one flashlight in each bus. We direct the light
output of each flashlight in the direction of the front windsheild of
each bus. The buses are each 10 meters in length and we also mount
two rulers on the inside of each bus that are exactly 10 meters long each.
The rulers are the same length as the buses are, so they run from the
very back to the very front, and have increments marked off at 1 meter
intervals on the rulers ( these are fairly long rulers ).

Since the photon is the basic particle of light, we only need
to look at one photon moving in order to understand how light travels.
When both flashlights are turned on one photon will travel inside each
bus from the back to the front so it eventually will exit the bus
out through the windshield.
The two flashlights will be turned on at the same exact point
(when the two buses rear bumpers align)
and the experiment will run from the time the two flashlights are
switched on untill the exact time at which the two photons exit
the two buses.

Of course one bus is parked and the other bus is moving at 0.87c, or
0.87 times the speed of light.

To illustrate how the speed of light can be constant even when something is moving
we track the two photons as they leave their respective special flashlights
and see what happens when one flashlight is traveling inside a bus that is moving
very fast and one flashlight is inside a bus that is not moving at all.

(See attached file)

In the slides each kind of object is color coded:
Blue indicates the buses' inside (rectangle) as viewed from the top.
Red indicates the ruler with increments marked at 1 meter intervals.
Green indicates the path each photon will follow.
A bright yellow dot represents a photon.
The gray arrow shows the direction of the lower bus in each slide, as well
as the direction of the photons. The top bus never moves, while the bottom bus
moves past the top bus at a speed of 0.87 times the speed of light.
Now we look at the slides which show what happens at 6 intervals of distance.
Each slide is enclosed within a brown rectangle and labeled "0" through "5".
The slide labeled "0" is the very start of the experiment.
The slide labeled "5" is the very end of the experiment.
The slides show where the moving bus is (lower) and where the photons are.

To start the experiment, the bottom bus speeds up to 0.87 times the speed of light
and starts to pass the top bus which is standing still.
Now as soon as the two rear bumpers align, both flashlights are signaled to turn on
and they emit exactly one photon each (refer to slide "0"). Since the flashlights
are at the back of each bus, one photon appears at the back of each bus at the
very instant the two buses' rear bumpers align. Each photon is represented by
a single yellow dot.
You will notice that the lower bus is only half as long as the top bus.
This is the lenght contraction that occurs when something travels fast.
The bus appears to be half as long to us, but to the person driving
the bus it still looks like the same size. You will notice the ruler is shorter
too, but notice it still has 9 marks on it. What is the distance between marks
if the ruler is shorter?
Well the distance as the stationary people (us and person in the upper bus)
see it is half of a meter, while the distance as the person riding the moving
bus sees it is still one meter.
To the person riding the moving bus, the ruler hasnt changed at all. To the
people not moving, the ruler shortened by 50%. This is what happens when
something moves. When something moves it travels in its own frame of reference
called its "inertial frame of reference".

Slide "0" is the point in time where the photons are just created and havent
traveled any distance yet, so they are still at the very back of the bus.
One bus is traveling so fast it is only half as long and so the front of that
bus only reaches to the center of the bus that isnt moving.
Even though the buses are now different lengths from our viewpoint, the two photons
are emitted at exactly the same point as we measure it, and so they start out
at the same place ( like a horse race starting gate ). Now if a photon moving in
a moving vehicle can travel faster then a photon moving in a stationary
vehicle, the lower photon in the fast moving bus should travel across our
field of view faster then the other photon. But that is NOT in fact what
happens. Instead look at slide 1 and see what happens.
Since the speed of light is a constant, the two photons reach the same place
in our view, as well as in the view of the person on the moving bus. Notice
also that the photon on the moving bus has now traveled exactly two units
to the right on its' own ruler, while the photon on the stationary bus has also
traveled exactly two units to the right on its' own ruler, yet the two photons
remain perfectly in sync. Remember you have to take into account that the
lower bus is moving. This is how all observers 'see' light acting the same.

You can probably guess already that if this was a horse race, it would be
a tie for first place. Indeed, both photons reach the windshield of each
bus at the same place ( see slides 1 through 5 ). Also, this occurs when
both buses front bumpers align, as shown in slide 5.

Now just in case you hadnt noticed, 'time' was left out of this discussion.
In order to understand how light appears to the person traveling fast
we need to consider how that person views time also.
Since the speed of the bus is 0.87 c and the speed of the photon is c
wouldnt the person riding on the moving bus see the photon traveling
along at the difference of these two speeds? Well to the moving
persons viewpoint, time slows down exactly the opposite of how
much that bus shortens due to the fast movement. The phonomenon of
how time slows down for that person is exactly the opposite as the
phonomenon of how that bus shortens, so when that person goes to
measures the speed of light, the speed comes out the same as when
we measure it. In other words, for the moving person the two effects
cancel each other and so light looks the same to both moving person
and stationary person.

When you look at the slides, notice both photons traveled the same
distance on their paths. It didnt matter how fast the flashlight
was traveling; once the photon leaves the flashlight, it forms its
own system and behaves like any other photon.

One thing i should point out here:

Although these slides really depict the intuitive view of the situation,
some problems would come up if we were to actually try this experiment.
Also, the Lorentz contraction of the bottom bus might not actually occur exactly
as depicted in the slides. Instead, there might be a bit more complex phenomenon
that actually happens in real life but these slides at least give the
general idea of how light seems to be the same to every observer.

Enjoy!

--Al

 

A good video, I think when we have the ability to know more about black holes. Bending space time could potentially allow us to to travel at the speed of light or faster. If time is not relevant then speed is of no issue.

https://www.pbs.org/video/black-hole-apocalypse-yj34qi/

kv

 

A good video, I think when we have the ability to know more about black holes. Bending space time could potentially allow us to to travel at the speed of light or faster. If time is not relevant then speed is of no issue.

https://www.pbs.org/video/black-hole-apocalypse-yj34qi/

kv

Even if it's mathematically possible and has a valid physical solution, the energy required is far beyond our current level of science.
https://en.wikipedia.org/wiki/Kardashev_scale

Dr. Liu is right on the money.
Time flies like an arrow, fruit flies like a banana!

 

Even if it's mathematically possible and has a valid physical solution, the energy required is far beyond our current level of science.
https://en.wikipedia.org/wiki/Kardashev_scale

Dr. Liu is right on the money.
Time flies like an arrow, fruit flies like a banana!

Much further in the future than we will ever know, if not possible I'm thinking will we pursue it? Maybe? it's in our genes we will pursue. So, will we continue to throw something against a wall to see the way it moves, stops or slows? Based on this "Thread" probability is we will continue. 3 billions years in the future is hard to calculate what will happen or won't. If all goes well then maybe there is a chance to find distant answers or find simply more questions that need answers. At this point only more questions.

kv

 

Hi,

I mispoke when in post #85 i said we cant calculate the speed of the moving bus form the diagram, but we can.
Notice when the photon moves 4 units to the right the moving bus only moves 2 units. That's half the speed of light.

 

I love the exploration of interesting propulsion... I've read bits about this... there are some other very theoritical and seemingly incredible engines being explored...

Just try to imagine when tesla and marconi claimed to be able to send things through the air and the moment bell was able to transmit sound on a wire! It was unthinkable and many thought it was a hoax... how could Tesla control a little boat by remote control... it's a hoax... magnets or hidden wires... beyond accepted science.

I believe there is an expenditure of energy in the the "flip flop" engine (for lack of better word)... I thought that a laser was used to change the mass of one side then the other and caused the change in mass... I can't read the article; you need a subscription.

Look at this article... they are making progress but we are all still not sure if it's entirely what is going on... but THIS is science or at least the leading edge... some of the other stuff is just history based on scientific discovery.

https://www.forbes.com/sites/starts...ace-engine-really-is-impossible/#ef56a073a009

so that's my $0.02

 

I love the exploration of interesting propulsion... I've read bits about this... there are some other very theoritical and seemingly incredible engines being explored...

Just try to imagine when tesla and marconi claimed to be able to send things through the air and the moment bell was able to transmit sound on a wire! It was unthinkable and many thought it was a hoax... how could Tesla control a little boat by remote control... it's a hoax... magnets or hidden wires... beyond accepted science.

I believe there is an expenditure of energy in the the "flip flop" engine (for lack of better word)... I thought that a laser was used to change the mass of one side then the other and caused the change in mass... I can't read the article; you need a subscription.

Look at this article... they are making progress but we are all still not sure if it's entirely what is going on... but THIS is science or at least the leading edge... some of the other stuff is just history based on scientific discovery.

https://www.forbes.com/sites/starts...ace-engine-really-is-impossible/#ef56a073a009

so that's my $0.02

The electromagnetic theory behind Tesla's boat was discovered long before Tesla used them. He was using applied science (engineering) from the science developed by Faraday, Maxwell and Hertz. There was nothing beyond previous science Tesla ever did and a lot on nonsense behind his so called energy discoveries.

From your link:
As humans, we may be easily fooled, but to fool nature is not so simple.

 

yep... but we keep trying...

 

yep... but we keep trying...

That's how we make scientific progress but

 

I have seen some incredible things that is still not explained by our current scientific discoveries... Doesn't mean it doesn't exist or breaks any of our "theoretical" laws... let's keep our minds open

I remember when more than half the stuff around me were in science fiction books

I never liked margarine.

 

The engine is not done:

June 2019:
https://www.wired.com/story/a-mythical-form-of-space-propulsion-finally-gets-a-real-test/

April 2019:
http://emdrive.com/

Test data:
http://www.emdrive.com/fm2test101.pdf

 

I have seen some incredible things that is still not explained by our current scientific discoveries... Doesn't mean it doesn't exist or breaks any of our "theoretical" laws... let's keep our minds open

I remember when more than half the stuff around me were in science fiction books

I never liked margarine.

Exactly what are those things?

 

The engine is not done:

June 2019:
https://www.wired.com/story/a-mythical-form-of-space-propulsion-finally-gets-a-real-test/

April 2019:
http://emdrive.com/

Test data:
http://www.emdrive.com/fm2test101.pdf

The EMDrive is dead and buried to all but the deepest fringe.

 

it's the same process that they use dried apple with artificial flavoring for my oatmeal and then take fig pieces to fake blueberries...

 

hmm... maybe dead but not buried... if this engine produces power from earths magnetic fields it may still be of use just not as originally intended.

 

The EMDrive is dead and buried to all but the deepest fringe.

Never thought I'd agree with you on this... but sadly, you're right. Some of us have a hard time letting go of dreams, even on the face of conclusive evidence.

And btw, I think I'm beginning to understand your photon rocket explanation, and the violation of conservation of energy in this case.

My mind's been wondering lately if it would be possible to build a device that could somehow sync with the virtual particles on the vacuum and use them to produce thrust.